Added the MPExpressionTree Classes

MathPad/MPOperatorChain.m

@@ -0,0 +1,75 @@
+//
+//  MPOperatorChain.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 11.10.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPOperatorChain.h"
+
+@implementation MPOperatorChain {
+    NSRange _range;
+}
+
+- (id)init
+{
+    self = [super init];
+    if (self) {
+    }
+    return self;
+}
+
+- (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
+{
+    self = [self init];
+    if (self) {
+        [tokenStream beginIgnoringWhitespaceTokens];
+        MPToken *currentToken = tokenStream.currentToken;
+        if (currentToken.tokenType != MPOperatorListToken) {
+            @throw [NSException exceptionWithName:NSInternalInconsistencyException reason:@"Expected Operators" userInfo:nil];
+        }
+        NSString *operatorString = currentToken.stringValue;
+        _range = currentToken.range;
+        operatorString = [[operatorString componentsSeparatedByString:@" "] componentsJoinedByString:@""];
+        _negating = NO;
+        _numberOfOperators = operatorString.length;
+        for (NSUInteger index = 0; index < _numberOfOperators; index++) {
+            if ([[operatorString substringWithRange:NSMakeRange(index, 1)] isEqualToString:@"-"]) {
+                _negating = !_negating;
+            }
+        }
+        [tokenStream currentTokenConsumed];
+        [tokenStream endIgnoringOrAcceptingWhitespaceTokens];
+    }
+    return self;
+}
+
+- (NSRange)range
+{
+    return _range;
+}
+
+- (BOOL)validate:(MPParseError *__autoreleasing *)error
+{
+    return YES;
+}
+
+- (NSDecimalNumber *)evaluate
+{
+    return self.negating ? [[NSDecimalNumber alloc] initWithInteger:-1] : [NSDecimalNumber one];
+}
+
+- (NSArray *)expressionElements
+{
+    NSMutableString *text = [[NSMutableString alloc] init];
+    for (NSUInteger index = 1; index < self.numberOfOperators; index++) {
+        [text appendString:@"+"];
+    }
+    if (self.negating) {
+        [text appendString:@"-"];
+    }
+    return @[text.copy];
+}
+
+@end